Solutes and Solvents

Solutes and Solvents

Middle School

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Learning Objectives

• Define and differentiate between a solute, solvent, and solution.

• Compare and contrast two types of mixtures: homogeneous and heterogeneous.

• Explain the important concepts of solubility and concentration.

• Describe how solutes affect the boiling and freezing points of a solvent.

Key Vocabulary

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Solute

The substance that is dissolved in a solution and is present in a smaller amount.

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Solvent

The dissolving substance in a solution, which is usually present in the largest amount.

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Solution

A mixture where a solute is evenly dissolved into a solvent, creating a uniform appearance.

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Solubility

The ability of a substance, the solute, to form a solution with another substance, the solvent.

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Concentration

A measure of the amount of solute that has been dissolved in a certain quantity of solvent.

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Mixture

A combination of two or more substances that are not chemically joined and can be separated.

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Understanding Solutions

Solute

• ​A solute is the substance that gets dissolved when making a solution.

• ​​It is the material that is present in the smaller amount.

• ​In saltwater, the salt is an example of a solute.

Solvent

• ​A solvent is the substance that does the dissolving in a solution.

• ​​It is the material that is present in the larger amount.

• ​In saltwater, the water is an example of a solvent.

Multiple Choice

In a sugar-water solution, what role does the sugar play?

• It is the solvent.

• It is the mixture.

• It is the solute.

• It is the solution.

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Types of Mixtures

Homogeneous Mixture

• ​These mixtures look the same all the way through, with a uniform appearance.

• ​​You cannot see the different individual components that make up the mixture.

• ​They are also known as solutions, and the substances are not chemically combined.

Heterogeneous Mixture

• ​In these mixtures, you can visibly see the different substances or parts.

• ​​The components are not evenly mixed, resulting in a non-uniform appearance.

• ​These parts can often be separated by simple physical methods like filtering.

Multiple Choice

Which of the following best describes a homogeneous mixture?

• A mixture with visibly different parts that can be filtered.

• A mixture where substances are chemically combined.

• A mixture that always involves a solid and a liquid.

• A mixture with a uniform appearance, also known as a solution.

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Types and Properties of Solutions

Types of Solutions

• The air we breathe is an example of a gas-in-gas solution.

• Soda is a common example of a gas-in-liquid solution.

• An aqueous solution is created when a substance is dissolved in water.

Properties of Solutions

• Water is called the 'universal solvent' as it dissolves many substances.

• In a true solution, the solute particles are stable and will not settle.

• These dissolved particles are so tiny they can easily pass through a filter.

Multiple Choice

Why is water referred to as the 'universal solvent'?

• Because it can dissolve many different substances.

• Because it only dissolves other liquids.

• Because it is the most common liquid on Earth.

• Because it is always the most abundant part of a solution.

Types of Solutions Based on Solubility

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Unsaturated

• It contains less solute than the maximum amount possible.

• You can still dissolve more solute in this solution.

• All of the solute particles are completely dissolved.

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Saturated

• It holds the maximum amount of solute that can dissolve.

• Adding more solute will not result in it dissolving.

• Undissolved solute may be visible at the bottom.

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Supersaturated

• It contains more solute than is normally possible to dissolve.

• This type of solution is unstable and not commonly found.

• It is created by heating and then slowly cooling a solution.

Multiple Choice

If you add sugar to your tea and it all dissolves, but you know you could dissolve more, what type of solution do you have?

• Supersaturated

• Aqueous

• Unsaturated

• Saturated

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Colloids and Suspensions

Colloids

• A mixture where small, undissolved particles are spread throughout but do not settle out.

• The particles are larger than in a solution, but too small to be seen easily.

• They are large enough to scatter a beam of light, like in milk or smoke.

Suspensions

• A mixture in which large particles are visible and can be easily seen.

• These particles will settle to the bottom over time or can be filtered out.

• Muddy water is a common example, where dirt particles settle in the water.

Multiple Choice

Which type of mixture is characterized by particles large enough to be seen that will settle over time?

• Solution

• Suspension

• Aqueous Solution

• Colloid

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Effects of Solutes

• When a solute dissolves, its particles are surrounded by the solvent particles.

• Ionic solutes in water can conduct an electric current.

• Solutes raise the boiling point of a solvent.

• Solutes lower the freezing point, causing ice to melt at lower temperatures.

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Multiple Choice

Based on the effects of solutes, why is salt spread on icy roads in the winter?

• It raises the freezing point of water, making ice melt.

• It raises the boiling point of the water, which melts the ice.

• It lowers the freezing point of water, preventing it from refreezing at 0°C.

• It makes the solution conduct electricity, which melts the ice.

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Concentration of a Solution

Low Concentration

• A solution with low concentration has a small amount of solute dissolved in it.

• These types of solutions are also known as dilute solutions.

• To make a solution less concentrated, you must add more solvent to it.

High Concentration

• A solution with high concentration has a large amount of solute dissolved in it.

• These types of solutions are also known as concentrated solutions.

• To make a solution more concentrated, you must add more solute to it.

Multiple Choice

If your glass of lemonade is too sweet (too concentrated), what should you do to make it less concentrated?

• Add more sugar

• Add more water

• Pour some of the lemonade out

• Add ice

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Common Misconceptions

Misconception	Correction
All mixtures are solutions.	Solutions are just one type of homogeneous mixture.
Dissolving is a chemical change.	Dissolving is a physical change, not a chemical one.
Once a solution is saturated, nothing more can be dissolved.	Heating a saturated solution can dissolve more solute.
Clear liquids are always pure substances.	A clear liquid can be a solution with dissolved parts.

Multiple Choice

Why does adding ethylene glycol (antifreeze) to water in a car's radiator help prevent the engine from both overheating in summer and freezing in winter?

• It lowers the boiling point and raises the freezing point.

• It only lowers the freezing point.

• It only raises the boiling point.

• It raises the boiling point and lowers the freezing point.

Multiple Choice

Which statement correctly describes a concentrated solution?

• It contains very little solute dissolved in the solvent.

• It has a large amount of solute dissolved in it.

• It can only be made by adding more solvent.

• It is the same as a dilute solution.

Multiple Choice

A student dissolves a large amount of a powder in hot water, creating a clear liquid. As it cools, the powder begins to form solid crystals. Analyze this process to determine what type of solution was formed.

• A colloid that separated into its parts.

• A saturated solution that became unstable.

• A supersaturated solution that became unstable as it cooled.

• An unsaturated solution that lost its solvent.

Multiple Choice

Imagine you have two unknown clear mixtures. Mixture A scatters a beam of light passed through it. Mixture B does not scatter light. What can you conclude about them?

• Mixture A is a solution and Mixture B is a colloid.

• Mixture A is a colloid and Mixture B is a solution.

• Mixture A is a suspension and Mixture B is a colloid.

• Both are solutions.

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Summary

• A solute dissolves in a solvent to form a solution.

• Mixtures are either homogeneous with a uniform look or heterogeneous.

• Solubility determines if a solution is unsaturated, saturated, or supersaturated.

• Colloids and suspensions have larger particles than solutions.

• Solutes raise a solution's boiling point and lower its freezing point.

• Concentration is the ratio of solute to the solvent in a solution.

Poll

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